1. Field of the Invention
The invention relates to a fuel cell.
2. Description of Related Art
A fuel cell includes a membrane electrode assembly (hereinafter referred to as an MEA) in which electrodes are joined to membrane surfaces of an electrolyte membrane, an anode passage, and a cathode passage, and receives supply of a fuel gas and an oxidizing gas supplied from the passages to generate electric power. In recent years, an expanded metal, which is formed by performing press-molding on a thin metal plate, is used frequently. In the expanded metal, an expanded passage in the shape of a mesh is provided so as to intersect with the direction of flow of a gas that flows from a gas supply side to a gas discharge side, and the expanded passage connects the gas supply side and the gas discharge side while winding. When the gas passes through the mesh-shaped passage, a pressure loss occurs when the gas passes through a bent portion of the passage, and the pressure loss tends to cause a reduction in the power generation performance of the fuel cell. To cope with this, a method for suppressing the pressure loss on the gas supply side is proposed.
In Japanese Patent Application Publication No. 2009-26472 (JP 2009-26472 A), in a fuel battery that includes the expanded metal, the expanded metal is formed such that the pressure loss of the gas on the gas downstream side is increased to be larger than the pressure loss of the gas on the gas upstream side, and unevenness in the amount of gas supplied to a power generating element is reduced without excessively increasing the pressure loss of the gas in the entire expanded metal. In addition, in Japanese Patent Application Publication No. 2010-170984 (JP 2010-170984 A), in the fuel battery in which a gas passage is formed of the expanded metal of the fuel battery, the gas passage is formed such that the gas flows without repeating a small turn, and the pressure loss of the gas is thereby reduced. At a turn position of a flow direction of the gas, the flow direction of the gas having arrived at the turn position changes, and hence the gas is locally directed to an electrode surface of the MEA or directed to a side away from the (electrode surface. As a result, at the turn position, the evaporation of water from the MEA or the penetration of water into the MEA occurs, the deterioration of humidity of the MEA may occur when the water evaporation is excessive, and flooding of the MEA may occur when the water penetration is excessive. However, in JP 2009-26472 A and JP 2010-170984 A mentioned above, these points are not considered. In addition, in the case where the expanded passage is the passage on a cathode side, an anode passage that supplies a hydrogen gas is present on an anode side across the MEA, but this relationship with the anode passage is not considered in JP 2009-26472 A and JP 2010-170984 A mentioned above. Thus, it is desired to suppress both of the pressure loss of the gas on the gas supply side and the flooding.